Three-phase transformer and protective device therefor



M 1937- H. A. w. KLINKHAMER ,2

THREE-PHASE TRANSFORMER AND PROTECTIVE DEVICE THEREFOR Filed Feb. 7, 1955 V 2 Sheets-Sheet 1 I/IIIIIA II: 7/ ll VIII/,1 YI/I up l A 4 lw I b '1 N A 7/////////// ///t VIII/I/I/l/I/I/I/A 'lI/I/I/I/IA I I nverofor: E67. wzrmmm Marph 2, 1937.

H. A. W. KLINKHAMER THREE-PHASE TRANSFORMER ANlj PROTECTIVE'DEVICE THEREFOR Filed Feb. 7, 1935 2 Sheets-Sheet 2 PM Mar. 2,1931

UNITED STATES PHASE TRANSFORMER AND 'rnass- PIOTEOHVI DEVICE OB Hendrik Abraham Wiinand Klinkhamer, lindhoven, Netherlands, asslgnor to N. V. Philips brlehen, lindhoven, Netherlands Application February I, 1985, Serial No? 5,640 In Germany February 12, 1984 iclaims.

1s windings of the transformer, unbalancing of the load will be caused by back ignition in one of the tubes. or the breakdown of a tube. In the case of back ignition of a tube, unless the circuit is interrupted, a permanent injury to the tube will result, whereas if one of the tubes becomes inoperative, a very great overloading of the r inin tubes, with resulting injury to same, takes place.

According to the invention a protective device 25 is applied to the transformer to interrupt the circuits whenever the load becomes unbalanced for whatever reason; this. protective device operat- 1:8 to insure immediate and automatic protecon. V

More specifically and lower yokes of the transformer and outside of the windings, a magnetically-operated contact device, which is actuated directly by the magnetic leakage field set up when an unbalanc- 35 ingoftheloedtakesplace,i.e., whenthesumof the secondary currents differs from sero.

In a preferred form of my invention I provide a magnetisable body disposed in the leakage. field of the transformer and which, when magnetised, 0 directly actuates contacts to interrupt the magnetisatlon of the transformer.

Iamawarethatithasalread'ybeenpropoeedto use protection devices controlled by the leakage field of a three-phase transformer to cause the 4s unbalancing of the load to deenergise the transformer. However. in prior art devices a special winding was provided in which, under the action of the leakage field, currents were induced and thesecurrentsintheirtumactuatedarelayto so interrupt the transformer circuit.

A protective device according to my invention has not only the advantage of greater simplicity and lower cost, but also of greater reliability, especially if the unbalancing of the load is con- 66 siderable and the created change in the leakage I provide between the upper field is large; this being, for instance, the case when, in the above-mentioned application, an unbalancing takes place due to the back discharge or inoperativeness of one of the tubes.

In order that the invention may be more clearly understood and readily carried into effect, it will be more fully explained in reference to the accompanying drawings, in which:

Figure 1 is a sectional side view of one form of contact device, suitable for the protective device of the invention.

Fig. 2 is an elevation of a three-phase transformer showing the protective device applied thereto.

Fig.3isasectionofl'ig. 2 along the line 1 Fig. 4 is a schematic diagram showing the device and circuits in accordance with the invention.

Fig. 5 is a schematic diagram showing the loadm side of Pig. 4 when using a single three-phase rectifier instead of three individual single-phase rectifiers.

Pig. 6 is a schematic diagram showing the connections of the contact devices, when two transa formers are used in parallel.

Pig. 7 is an elevation of a three-phase transformer provided with two protective devices.

Fig. 1 illustrates a contact device comprising a cylindrical envelope I, for instance, of glass, the lower end of which forms two chambers separated by means of an inwardly-projecting partition 80. Within the chambers are formed mercury pools I and-O respectively, which are connected to the outside by lead wires 1 and I re- 85 spectively, hermetically sealed through the envelope I.

The device is preferably exhausted or filled with an inert gas.

Arranged within the envelope l and supported by the upward bent portion of the bottom and guided therein by the wall of the envelope is a ferromagnetic member 2, which is shiftable in the direction of the axis of the device under the infiuence of a magnetic field. The ferromagnetic member 2 is provided with two contact strips 3 and 4, which in the lower or normal position of the member v2, .bridge through said member, the mercury pools I and t, and thereby close a circuit passing through leads 1 and 1. I

When member I is raised by magnetic force, the contact strips 3 and l stemmed from the mercury pools and the circuit is interrupted 'Io concentrate the ma netic field around the envelope i so as to act on the member 2, ferrou magnetic sleeve members, for instance in the form of iron tubes l2 and I3, surround the upper and lower portions respectively of the envelope I;

the tubes l2 and It being disposed in the magnetic leakage path of the transformer, as will be shown hereinafter.

Referring to Figs. 2 and 3, the three-phase transformer shown therein comprises a core consisting of three legs 35, 38 and 31, an upper yoke 8 and a lower yoke 9, the laminations of the yokes being held together, for instance, by means of angle pieces i0-l0', and H-il' (see Fig. 3). The legs of the transformer core are surrounded by coils l5, I6, and II respectively, each coil comprising a primary winding and a secondary winding.

Between coils i5 and I8 and secured to the pieces I 0 and II is arranged a contact device It which may be of the type shown in Figure 1; the leakage field being concentrated in a magnetic path of low reluctance by means of the ferromagnetic members I! and it, these being preferably soft iron tubings secured to the angle pieces I0 and II respectively and partly surrounding the device ll.

As under normal operating conditions the leakage field is negligible and practically no lines of magnetic force pass through the members i2 and If, these members need not be laminated.

The contact device It is so disposed that its magnetic member, for instance, the magnetic member 2 of the contact device of Figure 1, is so located in respect to the adjacent ends of members l2 and I3 that a maximum sensitivity of the device be obtained.

Under normal operating conditions, i. e., when the load is properly balanced and the sum of the secondary currents are equal to zero, the leakage field passing through the members I! and II is almost negligible and at least too weak to operate the magnetic member of the contact device.

The circuit controlled by the contact device remains thus closed. However, when the load becomes sufficiently unbalanced to set up a 45 strong leakage field, such field directly actuates the magnetic member of the contact device, which in turn causes the'circuit controlled thereby to deenergize the transformer.

The use of the contact device in a direct cur-- rent welding installation using three individual rectifier tubes is shown in the diagram of Fig. 4, in which the core 18 of .a three-phase transformer is provided with three star-connected primary windings 44, I, and 46, and three starconnected secondary windings 40, II, and 42. The invention is however also applicable to other multiphase and otherwise connected transformers. Arranged on the transformer in the manner above indicated is a contact device H. Forrectifying the secondary three-phase-current there are provided three single-phase rectifier tubes l8, l9, and 50, having anodes II, I2, and 53, and cathodes ll, 55, and 58 respectively. One end of each of the secondary windings 40,, and 42 are connected to the star point ll, which is also connected to the welding electrode II; the free ends of secondary windings being connected to the individual anodes of the rectifier tubes; the interconnected cathodes of which are connected to the work piece 51.

The means to deenergize the transformer upon the action of the protective device is illustrated as an example, by a three-pole magnetically-opferated switch 13 having an actuating coil li, a 7 plunger rod I4, and cooperating contact pairs 63-, 65-", "-48. Mounted on the plunger rod and insulating therefrom and from each other, are three contact bars ,ll, and II, which, when the switch is energized, bridge the contact pairs 63-, IMO, and 81-" respectively. The lower end of the plunger rod is provided with a device, shown as a notch I I, which engages a latch when the plunger rod drops into its lower position, and which retains it until manually released. The switch It is shown as being the main control switch, however, an additional main switch may be provided to connect contacts 64, 68 and O8 to the three-phase supply Ill. The contacts 83, O5, and 61 are connected to the free ends of the primary windings I, ll and 44, re-

. spectively, whose other ends are interconnected at the star point 41 and when the switch It is closed, the transformer is energized.

The switch coil It is connected in series with the contact device It and a source of current supply I l, which may be obtained from the three phase supply 10.

As long as the load is balanced the leakage field is insufllcient to cause the contact device to open its contacts, coil "is energized from source H, and the transformer is energized.

Upon the unbalancing of the load, due for instance, to a back discharge in one of the rectifier tubes, the leakage flux increases suflciently to cause contact device It to break the switch coil circuit, which results in the plunger dropping and deenergizing the primary windings of the transformer; the plunger 14 being retained by notch 8| until, after remedying the cause of the unbalancing, the plunger I4 is released.

Fig. 5 shows the right-hand or load portion of Fig. 4 for the case when a single three-phase rectifier tube 83, having anodes II, II and I, and a common cathode 81, is used.

I In case it is desired to operate from a common three-phase source, a plurality of such welding outfits in parallel-each having its own transformer-each of the transformers is provided with two contact-devices. The circuit arrangement for the protective devices is schematically shown in Fig. 6, in which two contact devices It and is are provided on transformer I and two contact devices 28 and 24 are provided on transformer II. Transformers I and II are of similar construction; transformer I being shown in Fig. '1 and being similar to the transformer of Fig. 2 except that two contact devices are provided.

The lead 1' of contact device I. is connected to one pole of a two-pole plug 2| and the lead I is connected through the coil" of a switching device, serving to disconnect'transformer I, to one side of a current source .28, whose other side is connected to the other pole of plug 2|.

Similarly, the lead 1' of contact device It is connected to one pole of a two-pole plug 2! and the lead I is connected through a coil II of .a

switching device, serving to disconnect transandIIaretobeusedthephigllisconnectedto socket 21, and plug It is connected to socket II. In this case coil II, and thus transformer I. is deenergized when either contact device it or 24 breaks its contact, and thus transformer II is deenergined when either contact device I! or It breaks its contact. Thus, if a defect occurs both coils 20 and 25 are deenergised and both transformers are cut out of circuit.

The operation of the device according tothe invention does not depend upon the shape of the current curve through the transformer secondary, which is important as in many cases, particularly when load impulses suddenly occur, the shape of this curve may differ essentially from a sinusoidal shapes While I have described my invention on hand of specific examples and specific application, I do not wish to be limited thereto, but desire the appended claims to be constrlmd as broadly as permissible in view of the prior art.

What I claim is:

1. In'combination; a three-phase transformer comprising a 001'8 having'three 1688 ml! two yokes, a secondary winding on each of said legs. a partial magnetic circuit formed between said yokes, said magnetic circuit having an interruption, and a protective device a movable magnetic member actuated by the leakage field set up when the sum of the currents in the secondary windings diflers from aero, to substantially bridge said interruption of the magnetic circuit.

2. In combination, a polyphase transformer comprising a core two yokes, three equal primary windings dishaving-threeequallegsand' ing of the load on said transformer.

.3. In combination, a polyphase transformer comprising a core having three equal legs and two yokes, three equal primary windings disposed one on each leg, and three equal secondary windings disposed one on each leg; and a protective device'disposed between said yokes and outside of said windings, said protective device comprising two ferromagnetic members separated by an-air-gap, and a magnetically-operated contact device disposed in the vicinity of said air-gap,

said protective device being actuated by the leakage fleld set up when an unbalancing of the load occurs.

4. In combination, a polyphase transformer comprising a core having three equal legs and two yokss, three equal primary windings disposed one oneach leg, and three equal secondary windings disposed one on each leg; a protective device disposed between said yokes and outside of said windings, said protective device comprising two ierrom lnetic sleeves separated by an air-gap, and a magnetically-operated mercury switch disposed within one of thesesl'eves and in the vicinity of the air-gap, said protective device being actuated by the leakage'fleld resulting from the unbalancing of the load on said transformer. 

